The present invention relates to a method of treating particulate materials in a fluidized bed reactor, and to a fluidized bed reactor for treating the same.
During operation of a fluidized bed reactor, for example, for heating fine grain coil in a fluidized bed, there is always a danger that a part of the supplied particulate material (either the fluidized bed material and/or the solid material to be treated such as for example the fuel) will be pneumatically carried out from the fluidized bed with the fluidizing gas prior to its intended or desirably complete reaction, for example prior to the complete burning of the grains of the particulate material grains. This takes place particularly for particulate material with very small diameter, and first of all when this material moves in the fluidized bed together with greater particles, since the dragging force of the fluidized bed stream is greater than the own weight of such particulate material.
Since for example in the event of heating of coal in fluidized bed the portion with smaller coal grains in the fuel supply is not small, the above mentioned phenomenon can lead to an undesirably low burning degree. The coal dust contents remaining in the flying dust is so high that an additional burning in a specially designed fluidized bed chamber is required. Naturally, such problems also take place during treatment of other particulate materials and conducting other reactions in the fluidized bed.
Moreover, there is also a problem in the uniformity of the particulate material supply when the fluidized bed reactors are very big and concentration gradient in the fluidized bed must be as small as possible over the entire fluidized bed for conducting proper chemical reactions.
It is known to supply particulate materials into fluidized bed reactors by throwing the same from above into the fluidized bed, for example with the aid of sprinklers arranged on the walls of the reaction chamber, as used, for example, for supply of nontreated coal. This method, however, has the disadvantage in the fact that it results in a limited radius of action and more or less visible separation effect in the event of strongly controlled grain composition of the particulate material by formation of different trajectory throwing parabolas and by air sifting.
It is also known to provide falling shafts in the region of the top of the fluidized bed reactors. In this case the delivery of the particulate material is only of a point type and possible in such regions which are located below a solid top. Since very often the flue gas withdrawal requires considerable space in the region of the top, a uniform delivery in the construction with the falling shafts is possible only in the event of lateral arrangement of flue gas withdrawal means.
Finally, it is known to supply the particulate material with the aid of screws and air nozzles into the lower part of the fluidized bed. In this case, a stream pipe extends with its mouth tightly through the bottom of the fluidized bed. This construction has a disadvantage in the fact that a supply of the particulate material must be carried out at the pressure level of the fluidized bed reaction and also many nozzles are required for uniform feeding. Moreover, the particulate material must be relatively finely ground which, in the event of fuel can cause the danger of self-ignition in the supply conduits. Finally, at the supply locations, gas bubbles or streams can be formed which travel up to the fluidized bed upper surface. As a result of this, the reaction time for particles entrained by the gas bubbles and streams is undesirably short.